Western Newt is the vernacular name for the
genus Taricha of which there are three species: torosa,
granulosa, and rivularus. These are toxic salamanders found
exclusively in particular regions of California, the western halves of
Oregon and Washington, and western costal Canada up through parts of Alaska
(3).
Being
newts, they are salamanders that spend the majority of their time on land
(2). Ideal places to find them are rock crevices and logs though
when breeding they prefer slow moving pools along costal streams.
While they resemble the rough skinned newt they can be distinguished in a
few ways. The clearest way is to note that California Newts have
lighter colored lower eyelids that match the color of their bellies.
They also have lighter color backs and larger eyes that protrude outside the
width of the head when looking from above. California Newts prefer
more humid areas as well. Their bodies are not slimy, though they may
appear so when in and out of breeding pools. Rather, they are usually warty
and may approach eight inches long, the larger end for a newt (1). Most notably however, is the
toxicity of California Newts--the most toxic of poisonous newts (3).
image source:
http://www.npwrc.usgs.gov/narcam/idguide/range58.gif

Not for Human Consumption

The toxin exhibited by Taricha torosa is known as
tarichatoxin or tetrodotoxin (TTX), the same neurotoxin found in
pufferfish (3,5). While researchers were not sure if
these were the same, research has been confirmed that they are,
biochemically speaking. Tarichatoxin has 1% of the potency of TTX, the
more potent, water soluble variant.
The pure active ingredient's chemical structure is shown here.
All poisonous newts have a form of TTX that varies in potency with species (Taricha
is the most potent, Triturus is the least potent) and age
(juveniles are several times more potent than adults) (3).

In addition to curling its tail away from its
head when feeling threatened, California newts will secrete this toxin
through their granular skin glands (3). Therefore it is recommended
that they not be touched with bare hands or at least that hands be washed in
the event of contact. Oral ingestion is the more common route of
toxicity. One newt is enough to cause serious problems in humans if
ingested. While this may sound silly, there is a chance of human
ingestion as at least one case has been documented . A toddler once
fatally consumed a portion of the tail of an Oregon Rough Skinned Newt--a
species somewhat less toxic than the California Newt but still harmful (7).
Thus it is not inconceivable that similarly curious dogs, raccoons, or other
mammals might try a bite...

Within 20 minutes to three hours of ingestion
symptoms of TTX may appear as hypertension, respiratory paralysis, and nerve
unresponsiveness at high dosages. Less extreme effects may be felt as
numbness and tingling. Though paralyzed, a victim of TTX poisoning
will still be conscious. This is caused by site specific binding of
TTX to voltage gated sodium ion channels in the nervous tissues. Any
binding to the extracellular pore opening of this ion channel inactivates it,
blocking sodium ion flow (4).
There
are two types of these ion channels--those with high affinity for TTX and
those with low affinity for TTX. Those with low affinity are primarily
in cardiac tissue while ion channels with high affinity for TTX are
distributed throughout the rest of the body. Based on this information
it can be expected that cardiac arrhythmia would result from higher doses.
A secondary effect of this toxicity is the inability of brain cells to
receive oxygen properly resulting in a lightheaded feeling and overall
weakness (3). A mouse bioassay has been developed to monitor TTX in
pufferfish though the only recommendation for treatment is assisted
respiration (5).

It is suspected that the newts acquire their
toxicity by ingesting or otherwise acquiring bacteria such as Vibrio spp
(3).
Likewise, some common garter snakes, Thamnophis sirtalis, may become
poisonous by ingesting Taricha granulosa.
They
are able to prey on the rough-skinned newt for the same reason the newts are
able to tolerate their own toxin. A point mutation in the gene that
codes for the sodium ion channel of concern has rendered certain snakes' ion
channel functional and completely resistant to TTX. This does not make
the garter snake venomous, only poisonous. A poisonous garter snake
will do no more harm when biting since it still does not possess venom
producing glands. It becomes harmful, however, when eaten by its
predators such as birds and mammals. This evolution in snakes then can
be used to observe toxicokinetics of TTX. For example, three weeks
after ingesting one newt it was observed that an average of 42 micrograms of
TTX remained in a snake's liver (6).
http://www.mikeredmer.com/Thamnophis_sirtalis_H3578_preview.jpg